Adherence

The extent to which the patient adheres to the advice or treatment offered in health-care consultations has been widely studied. Most medical consultations result in the prescription of treatment or advice, and the appropriate adoption of self-care behaviours, including use of medicines, is a key aspect to the self-management of most chronic illnesses. However, many patients fail to do this and low rates of adherence to recommended treatment are seen as problematic in chronic physical and psychiatric illnesses.(96)

The incidence of reported medication non-adherence varies greatly from 4 per cent to 92 per cent across studies, converging at 30 to 50 per cent in chronic illness. (9Z> In the area of primary prevention, it has been found that many participants drop out of lifestyle-change programmes designed to improve diet or reduce health-risk behaviours.(98) Even patients who have experienced major health problems, such as heart attacks, may show low levels of uptake of rehabilitation programmes as well as considerable variation in the adoption of recommended lifestyle change. (5.§> In the area of mental health, there is also evidence of significant rates of non-adherence to various recommendations from health-care providers. For example, about half of those given an initial appointment at a mental health clinic were found to fail to attend for the first arranged interview, and approximately three-quarters of psychotherapy patients have been found to drop out by the fifth session of treatment.(99)

Although adherence may be simply defined as: 'the extent to which the patient's behaviour coincides with the clinical prescription', (1°0) there are several conceptual and methodological issues. For practical purposes non-adherence is usually defined as the point below which the desired preventative or therapeutic result is unlikely to be achieved. The percentage adherence necessary to achieve the desired effect varies between treatments and between and within individuals. Many individuals, particularly those with chronic health problems, are required to adhere to a variety of recommendations from their doctor. For example, diabetic patients are required to take medication, control their diet, and check their feet and blood glucose levels on a regular basis but it has been found that these behaviours are not highly correlated.(101)

Non-adherence behaviours may be categorized as either active or passive. Active non-adherence arises when the patient makes a strategic decision not to take the treatment as instructed. An example of this type of behaviour was found among hypertensive patients who believed that they could judge when their blood pressure was high by the presence of symptoms such as stress or headache and thus took antihypertensive medication only when these symptoms were experienced.(39) From a self-regulatory perspective, the level of treatment adherence may be indicative of a strategic coping response which is entirely consistent with the patient's view of their problem. Thus, patients who believe that their problem will not last for long have been found to be less likely than those with a more chronic time-line representation to adhere to their medication over a long period of time. (102)

Passive non-adherence may be unintentional when the patient's intentions to follow treatment recommendations are thwarted by barriers such as forgetting, and inability to follow treatment instructions because of a lack of understanding or physical problems such as poor eyesight or impaired manual dexterity. Thus, if the quality of communication is poor and patients receive information which is difficult to understand or recall, as has been outlined above, then this makes it less likely that treatment will be adhered to.(64)

Measuring adherence

Adherence measures can be divided into two broad categories according to whether the assessment is indirect or direct. Common indirect methods include self-reports from patients as well as seeking information from significant others such as spouses and other family members. Research indicates that patient reports are more accurate than estimates from doctors or family members but all such reports overestimate the true level of adherence. (103) Other indirect methods include counting pills and bottles and recording pill use with mechanical devices. Pill counting has the advantages of being technologically simple and inexpensive. However, some studies have shown that pill counts may also underestimate the true level of non-adherence. (104) In recent years technological developments have allowed the incorporation of electronic devices into the medicine container to record the time and date of usage. The major advantage of these devices is that they potentially provide a profile of medication taking rather than simply detailing how much was taken. (!°4) However, as with the pill-counting method, a dose removed is not necessarily a dose taken.

Direct measurement include blood and urine analyses which confirm the presence of a drug in the body and its concentration. However, these techniques are problematic partly because they may be difficult to carry out for many medications and partly because there is not a one-to-one relationship between the amount of medication or tracer taken and the concentration found in body fluids. Furthermore, a major drawback of direct methods is that they are invasive, expensive, of questionable reliability, and provide no indication of the type or time course of non-adherent behaviour.

The determinants of non-adherence

The search for causal factors to explain patients' adherence or non-adherence to their recommended treatment or advice has progressed through different phases over the last 20 to 30 years.

Much of the early work focused on the possible contribution of the demographic or personality factors as well as characteristics of the disease or treatment itself. In an early systematic review of 185 studies,(!05,) no clear relationship emerged between race, gender, educational experience, intelligence, marital status, occupational status, income, and ethnic or cultural background and adherence behaviours. Moreover, there is little evidence that adherence behaviours can be explained in terms of personality characteristics. ^M0.7 Also the idea that stable sociodemographic or dispositional characteristics are the sole determinants of adherence is discredited by evidence that an individual's levels of adherence may vary over time and between different aspects of the treatment regimen. (108) This limitation also applies to the search for disease and treatment characteristics as antecedents of adherence since there are wide variations in adherence between and within patients with the same disease and treatment.(108)

One very obvious explanation for non-adherence arises from poor understanding and recall of information presented in the medical consultation. Many patients lack basic knowledge about their medication^..09) but the relationship between this and their adherence is neither simple nor clear-cut. In a systematic review of the adherence literature, Haynes(!10) concluded that, although 12 studies had demonstrated a positive association between knowledge and adherence, there were more that had failed to demonstrate a link. Moreover, interventions that enhance knowledge do not necessarily improve adherence. (H1)

There is increasing interest in the role of patient satisfaction as a mediator between information provision, recall, and adherence. General satisfaction with medical care seems to have little relationship with adherence, but unfulfilled expectations with the treatment, the medical consultation, and the doctor do result in low adherence rates/11.2) In a national survey in the United Kingdom of patients' satisfaction with medicines information, over 70 per cent of respondents wanted more information than they were given. (H3) Dissatisfaction with attributes of the practitioner or the amount of information and explanation provided may act as a barrier to adherence by making the patient less motivated towards treatment/1!4)

The emphasis of adherence research over the last decade or so has moved away from attempts to identify stable trait factors which characterize the non-adherent patient to achieving a greater understanding of how and why patients decide to take some treatments and not others. Much of this research is informed by psychological theories which conceptualize behaviour as the product of cognitions which occurs within a social framework.

The application of social cognition models in research indicates that medication non-adherence may arise from a rational decision on the part of the patient and identifies some of the cognitions which are salient to these decisions. Although there is some variation in the specific type of beliefs which are associated with adherence across studies, the findings show that certain cognitive variables included in the Health Belief Model (28) and the Theory of Planned Behaviour(29) appear to be prerequisites of adherence in certain situations. For example, beliefs that failure to take the treatment could result in adverse consequences and that one is personally susceptible to these effects tend to be associated with higher adherence. (115) Perceived severity of anxiety has also been found to be related to adherence to recommended practice of relaxation training at home.(U6) Additionally, adherence decisions may be influenced by a cost-benefit analysis in which the benefits of treatment are weighted against the perceived barriers. (il511Z) Other studies, based on the Theory of Planned Behaviour have shown that the perceived views of significant others such as family, friends, and doctors (normative beliefs) may also influence adherence. (H8) Several studies have demonstrated the value of interventions based on the Health Belief Model in facilitating health-related behaviours, such as attending for medical check-ups, (1.19) or using emergency care facilities in an acute asthma attack/120

Another cognitive approach which has been used to explain non-adherence is the self-regulatory model outlined earlier. This model also acknowledges the importance of symptom perception in influencing illness representations and adherence as a coping behaviour. Confirmatory evidence for this is provided by findings from a study of patients with diabetes who used perceived symptoms to indicate their blood glucose levels and to guide self-treatment. (63) However, patients' beliefs about their symptoms, and estimations of their own blood glucose levels were often erroneous and resulted in poor diabetic control. In studies of non-insulin-dependent diabetic patients, Hampson (121) has shown that personal models of diabetes are related to dietary self-management and to exercise adherence but not to the more medical aspects of control, such as blood glucose testing and taking medication.

Recent research has begun to focus on the role of people's beliefs about medicines and the ways in which these could influence adherence. Work by Horne (54) indicates that four 'core themes' or factors underlie commonly held beliefs about medicines. Factor analysis of a pool of belief statements revealed two broad factors describing people's beliefs about their prescribed medicines: their perceived necessity for maintaining health ( specific-necessity) and concerns based on beliefs about the potential for dependence or harmful long-term effects and that medication taking is disruptive ( specific-concerns). Two factors were also found to describe people's beliefs about medicines in general. The first relates to the intrinsic properties of medicines and the extent to which they are harmful addictive substances (general-harm) and the second factor comprises views about whether medicines are overused by doctors (general-overuse).

People's views about the specific medication regimen prescribed for them were found to be much more strongly related to adherence reports than are more general views about medicines as a whole. Moreover, an interplay was found between concerns and necessity beliefs which suggests that people engage in a risk-benefit analysis and consequently attempt to moderate the perceived potential for harm by taking less. Patients with stronger concerns based on beliefs about the potential for long-term effects and dependence reported lower adherence rates, whilst those with stronger beliefs in the necessity of their medication reported greater adherence to medication regimen/54 This work points to the importance of accessing patients' beliefs as a prerequisite of any intervention designed to increase medication adherence. In particular it would seem important to identify specific concerns about treatment and to allay these in ways which make sense to the patient.

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